1. Field of the Invention.
The field of the invention is electronic controllers for controlling industrial machines and processes, and more particularly memory cartridges for circuit board modules used in such equipment and controllers.
2. Description of the Prior Art
Industrial controllers are typically connected to assembly line equipment and process control equipment in manufacturing facilities and other industrial plants. Smaller controllers, including programmable controllers, have typically been built as a set of modules that are inserted in a rack somewhat like a set of books placed side-by-side in a bookcase. These modules may include a main processor (CPU) module, communication modules and I/O interface modules.
I/O interface modules were originally developed as an isolation interface between the logic-level signals of the industrial controller (e.g. 5-volts DC) and the power-level signals (e.g. 120-volts AC) being supplied to the devices on the industrial equipment being controlled. More recently, these I/O modules have included peripheral processors which may perform very sophisticated control functions with periodic communication with the main processor (CPU) module.
In main processor modules it has been known to provide some type of replaceable programmable read-only memory (PROM) circuits so that the module can be reprogrammed. In some instances such PROM's have been placed on a small circuit board and within a small housing.
Where many different programs of a moderate complexity are to be stored and executed, it is desirable to store and execute them in random access memory (RAM). This allows convenience in loading, testing and debugging such programs. With cartridges, the programs can be developed with off-line development systems and later installed in the controller equipment.
Whereas PROM circuits are non-volatile, RAM circuits are volatile--their contents are lost when power is turned off. Many products therefore provide battery back-up for RAM circuits.
RAM cartridges have not been widely used, perhaps due to the size and complexity required in such a cartridge and the need to provide convenient installation.
There is a need to provide a RAM cartridge in a package that is convenient to install and remove from a circuit board module in industrial controller equipment. In such a cartridge, there is also a problem of the cartridge housing blocking the escape of heat both from the circuits in the cartridge itself and from the circuit board module into which the cartridge is installed.